Prior Art-related Description
In this 1966, a surface recording density of the hard disk drive (HDD) has been in excess of 1 Gbit/square inches. It is an MR (magnetoresistive) head having a reproducing output higher than the conventional thin film head that acts as a motive power. However, for several recent years, the surface recording density of the HDD has continued to increase at the rate of 60% a year, for example.
According to the request to continue to improve the sensitivity of the magnetic head, the giant magnetoresistive film (GMR film) which can output a high read signal has been watched with interest. Since the spin valve magnetoresistive film can be formed relatively easily because of its relatively simple structure and the rate of change of the electric resistance at a low magnetic field is higher than the normal MR device, recently attention has been paid to the spin valve magnetoresistive film out of the GMR films.
The MR head uses an MR film whose resistance is varied by applying the external magnetic field as a reproducing head. The magnetic field (external magnetic field) generated from the recording medium is detected as the resistance change and then output as the voltage change. In the GMR head, the MR film is replaced with the GMR film.
The magnetic heads using the spin valve magnetoresistive film (referred to as the "spin valve head" hereinafter) have been set forth in U.S. Pat. No. 5,206,590, Japanese Patent Application Publication (KOKAI) Hei 6-60,336, and French Patent FR No.95-5,699.
FIG. 1A is a schematic plan view showing an example of such spin valve head, FIG. 1B is a sectional view showing a sectional structure taken along a line B--B in FIG. 1A, and FIG. 1C is a sectional view showing a sectional structure (structure opposing to the recording medium) taken along a line C--C in FIG. 1A.
As shown in FIG. 1B, a spin valve head 110 is a composite magnetic head. The composite magnetic head comprises a reproducing head 122 and a recording head 123 if classified roughly, and is formed as a piggyback structure in which the recording head 123 is attached on a back portion of the reproducing head 122. An upper reproducing shielding 109 of the reproducing head 122 and a lower recording magnetic pole (lower core) 109 of the recording head 123 are used commonly as a merge type magnetic head.
As shown in FIGS. 1B and 1C, the reproducing head 122 uses a spin valve film 111. The reproducing head 122 comprises the spin valve film 111, a lower reproducing shielding 108 arranged via the spin valve film 111 and a lower reproducing gap film (insulating layer) 115, and an upper reproducing shielding 109 arranged via an upper reproducing gap film (insulating layer) 116.
The recording head 123 comprises a recording coil 120, a recording gap film (insulating layer) 118 for surrounding the recording coil 120, a lower recording magnetic pole (upper magnetic pole) 109 placed on both sides of the insulating layer, and an upper recording magnetic pole (upper core) 119. The recording coil 120 is buried in the insulating layer 118.
In this manner, the reproducing head 122 and the recording head 123 are formed integrally with each other in the composite magnetic head. But normally the composite magnetic head in which the spin valve head 110 is employed as the reproducing head 122 is called the "spin valve head" 110 simply as a whole.
FIG. 1C is a sectional view of a sectional structure of the spin valve head 110 if viewed from the recording medium side (not shown). Upper and lower gap films (insulating films) 115, 116 are provided between the lower reproducing shielding 108 and the upper reproducing shielding 109. The spin valve head 110 is placed in a window between these insulating films.
The spin valve head 110 is patterned into a planar rectangle after film formation, and a hard film 106 and electrode terminals 107 are formed in two regions near both ends of the uppermost layer respectively, whereby the spin valve head 110 is finished.
In such a spin valve head 110, an area formed between a pair of electrode terminals 107 provided on both sides of the spin valve film 111 can act as a signal detecting region (sense region).
In this disclosure, for convenience of explanation, in order to specify easily the magnetization direction in the context of the spin valve head 110, a thickness direction of the spin valve film 111 (laminating direction) is defined as a Z-direction, a direction connecting the pair of electrodes 107 is defined as an X-direction, and a direction which intersects orthogonally with a Y-Z plane is defined as a Y-direction, as shown in Figures.
Manufacture of the spin valve head 110 as shown in FIGS. 1B and 1C is carried out in brief according to the following steps.
(1) Formation of the lower reproducing shielding 108 PA1 (2) Formation of the lower reproducing gap film 115 PA1 (3) Formation/patterning of the spin valve film 111, and formation of the electrode film 107 PA1 (4) Formation of the upper reproducing gap film 116 PA1 (5) Formation of the upper reproducing shielding/lower recording magnetic pole 109 PA1 (6) Formation of the recording gap film 118 PA1 (7) Formation of the recording coil 117 PA1 (8) Formation of the upper recording magnetic pole 119 PA1 (9) Formation of the protection film
FIGS. 2A to 2D are views showing the above step (3) of forming/patterning the spin valve film 111 and forming the electrode film 107 out of the steps of manufacturing such a spin valve head 110 in brief.
As shown in FIG. 2A, the spin valve film 111 is formed on the substrate (i.e., the lower reproducing gap film consisting of the insulating layer) and then thereon is formed a resist 114 having a two-layered overhanged structure consisting of a resist 112 and alumina 113.
Then, as shown in FIG. 2B, the spin valve film 111 is patterned into a planar rectangle by virtue of ion milling.
Then, as shown in FIG. 2C, the hard film 106 and the electrode film 107 are formed.
Finally, as shown in FIG. 2D, the resist 114 having a two-layered overhanged structure is lifted off. Thereafter, the process continues to the step of forming the upper reproducing gap film.
FIG. 3 is an enlarged sectional view equivalent to a portion enclosed with a circle in FIG. 2D in an enlarged fashion. In other words, FIG. 3 is a fragmentarily enlarged view showing a junction portion between the spin valve film 111 and one of the electrode terminals 107 when viewed from the recording medium.
The spin valve film 111 is formed over the lower reproducing shielding 108 via the lower reproducing gap film (insulating film) 115. The spin valve film 111 has an underlying layer 101, a free magnetic layer (free layer) 102, a nonmagnetic metal layer 103, a pinned magnetic layer (pined layer) 104, and an antiferromagnetic layer 105. A hard magnetic layer (hard film) 106 and an electrode film 107 formed on the hard film 106 are formed in the neighborhood of the side end portion of the spin valve film 111. The upper reproducing shielding 109 is provided over the spin valve film 111 and the electrode film 107 via the lower reproducing gap film (insulating film) 116.
In such spin valve head 110, the antiferromagnetic layer 105 is provided on the pinned layer 104 and then the pinned layer 104 is magnetized by the antiferromagnetic layer 105 in a direction opposite to the magnetization direction of the antiferromagnetic layer 105. Magnetic domains of the free layer 102 are controlled by the electrostatic magnetic field generated from a pair of hard films 106 arranged near the both ends of the free layer 102 to be directed in one direction.
Study of Problems of the Above Spin Valve Made by the Inventors
However, in the spin valve head 110 in the prior art as shown in FIG. 3, such a problem has arisen that Barkhausen noises are generated in the output of the spin valve head in response to the signal magnetic fields.
The inventors of the present invention have studied the cause of generation of Barkhausen noises based on the configuration of the spin valve head 110 shown in FIG. 3. For the magnetic domain control, since magnetic domains of the pinned layer 104 are controlled very strongly by a negative exchange interaction of the antiferromagnetic layer 105 which is coated on the overall surface of the pinned layer 104, no troubles occur in the pinned layer 104. In contrast, the magnetic domains of the free layer 102 are controlled very weakly by the hard film 106 placed only on both sides of the free layer 102. Therefore, it has become an issue whether or not the magnetic domains of the free layer 102 are controlled ideally by the hard film 106. Subsequently, if the configuration of the spin valve head 110 shown in FIG. 3 has been studied, a positional relationship between the free layer 102 and the hard film 106 has been able to be supposed as the cause for the above.
FIG. 4 is a schematic view showing the positional relationship between only the free layer 102 and the hard film 106 of the spin valve head 110 shown in FIG. 3. Where the magnetization direction of the hard film 106 is directed from the left side to the right side on the sheet of FIG. 4, therefore the magnetic domains of the free layer 102 are also controlled to be directed from the left side to the right side on the sheet of FIG. 4.
As shown in FIG. 4, it is to be understood that, in the spin valve head 110, the hard film 106 is formed to overlap with a part of the free layer 102 of the spin valve film along the Z-direction (thickness direction of the spin valve film). According to such hard film 106, magnetic charges of the hard film 106 are concentrated onto a top end portion of the hard film on the free layer side. As a result, it has been found that, in the region of the free layer 102 beneath the hard film 106, the direction of the magnetic field generated from the concentrated magnetic charges radially is directed oppositely to the free layer magnetization direction and thus there exists "reverse magnetic field region". Then, the inventors have examined the law of cause and effect between the presence of this reverse magnetic field region and the generation of the Barkhausen noise.
FIG. 5 is a view showing the distribution of magnetization in the free layer plane of the spin valve film 102 obtained by virtue of micromagnetics simulation. As shown in FIG. 5, the magnetization direction in the reverse magnetic field region where a part of the hard films 106 are overlapped is directed largely differently from the magnetization direction in the vicinity of the central portion. In other words, it has been understood that "magnetic domain control incomplete regions" exist in the free layers 102 which overlaps with a pair of hard films 106 respectively. FIG. 5, the magnetic domain control incomplete region on the left side corresponds to the reverse magnetic field region shown in FIG. 4, while the magnetic domain control incomplete region on the right side corresponds to the reverse magnetic field region omitted from FIG. 4.
FIG. 6 shows the response output voltage characteristic of the spin valve head, which has the incomplete single magnetic domain state (i.e., a number of magnetic domain state) having various magnetic field directions, to the recording medium signal magnetic field, obtained by virtue of the micromagnetics simulation. It is appreciated from FIG. 6 that, in the output voltage characteristic, very apparent hysteresis phenomenon has appeared in the range of the recording medium magnetic field from -150 to 120 oersted (Oe).
More particularly, if an external magnetic field is applied to the free layer 102 in the situation that a number of magnetic domains (i.e., small area having the same magnetization direction) exist in the free layer 102, the magnetization directions are rotated all at once so that the magnetization directions in the free layer are directed in one way uniformly. That is, a number of magnetic domains are changed to a single magnetic domain. It has been found that, if such spin valve film is employed as the magnetic head, the Barkhausen noise is superposed on the output waveform.
Hence, in order to prevent the Barkhausen noise, the inventors have examined a means for suppressing fluctuation of the magnetization direction in the free layer and for fixing always the free layer as a single magnetic domain.